This feature is required to link to the compiler_builtins crate which contains
"compiler intrinsics". Compiler intrinsics are software implementations of basic
operations like multiplication of u64s. These intrinsics are only required on
platforms where these operations don't directly map to a hardware instruction.

You should never need to explicitly link to the compiler_builtins crate when
building "std" programs as compiler_builtins is already in the dependency
graph of std. But you may need it when building no_stdbinary crates. If
you get a linker error like: